Thread: Do I need a BCDC charger?

Originally Posted by Milton477

40A from my D4 across 25mm2 cable to the van.

What in your van draws 40A? Do you have house batteries in the van?
6mm2 will carry 40A, just. I'd derate it to 10mm2. That's good for 54A. 25mm2 is rated at 97A.

Originally Posted by Mick_Marsh

What in your van draws 40A? Do you have house batteries in the van?
6mm2 will carry 40A, just. I'd derate it to 10mm2. That's good for 54A. 25mm2 is rated at 97A.

Purely to recharge the house batteries while travelling.
Bigger cable means less volt drop means quicker charge.

Originally Posted by Milton477

Purely to recharge the house batteries while travelling.
Bigger cable means less volt drop means quicker charge.

That was my reason for my 25mm2 cable also

Hi again John and the maximum current draw you are likely to see, with one very low 130Ah battery is about 40 to 45 amps + what ever your fridge draws, if you are running one.


If you had two 130Ah batteries in a low state of charge, then initially your could see MAYBY as much as a 70 amp draw.


Even if you had three 130Ah house batteries, in a low state, 70 amps is about the maximum current draw you will see.


The limitation at this point is the output capacity of your alternator.


By the time you deduct the power needed to run your disco, and any power needed to charge the first auxiliary battery if it was low, then you would be lucky to see 50 to 60 amps at the rear batteries.


The thicker cable you have run, means that can easily increase the auxiliary/house battery capacity with out needing to do any upgrading of your cabling.


You have literally future proofed your setup.


There is a lot more to this and I will be doing a companion to what you can expect if you go with a DC/DC device.

Basic electrical interconnection of car auxiliary and/or trailer batteries to the crank battery do work provided isolation is taken care of, so it is never a clear case of “needing” a DC DC charger.

i have heeded the recommendations of people like Colyn Rivers in that DC DC chargers do optimise the charging of each battery. I have solar panels on both camper trailer and car and needed MPPT solar controllers for both the camper and car auxiliary batteries, so it was a straightforward choice to put combined DCDC/MPPT units on both.

I am very happy with the setup, and confident that my crank battery is never being discharged to feed the other batteries, particularly when the engine is not running. If the DC DC charger is sized correctly, it will usually deliver plenty of charge and will never exceed the recommended charging rate. The limit on charge rate is about the only operational criticism leveled at DC DC UNITS.

NEIL

Originally Posted by Nmritchie

....

I am very happy with the setup, and confident that my crank battery is never being discharged to feed the other batteries. ....

I'm curious as to why you'd think that?
What makes you think that the crank battery is being 'discharged' to feed the other batteries?

Wouldn't the second battery in a dual setup or trailer be drawing on the first battery, which was then being recharged by the alternator and/or solar?

Originally Posted by AK83

I'm curious as to why you'd think that?
What makes you think that the crank battery is being 'discharged' to feed the other batteries?

Hi Arthur and what Neil is referencing to is the way my isolators allow up to 50% of the cranking battery’s capacity to be used to assist the auxiliary battery to power accessories while camping.